This invention relates to an acrylic fiber generally suitable to applications such as a garment and a home furnishing especially pile fabrics.
An acrylic fiber suitable to garments is required to have a good balance between its strength, elongation and dyeability.
An acrylic fiber is generally prepared by wet spinning. It has been a conventional practice to increase a ratio of (a drawing rate of a coagulated filament)/(a discharge linear velocity of a spinning feed solution from a spinneret capillary) in a coagulation bath and to increase a draw ratio in a subsequent step for achieving a high-strength fiber with high orientation.
However, increasing a ratio of (a drawing rate of a coagulated filament)/(a discharge linear velocity of a spinning feed solution from a spinneret capillary) in a coagulation bath, i.e., increasing a drawing rate of a coagulated filament, means a shorter coagulation time for a spinning feed solution in the coagulation bath. Coagulation and stretching, therefore, simultaneously occur in the coagulation bath, resulting in formation of a skin layer in a coagulated filament, which leads to inadequate solvent displacement inside the fiber.
Thus, the surface of the fiber has a higher fibrillated and highly oriented structure, while its inside has a coarse structure without fibrillation. When stretched with a high stretching ratio, a product becomes a fiber with a poor elongation, which will give a cloth with a stiff hand feeling. A fiber with an uneven orientation between its surface and inside provides a poorly elastic staple fiber, which will give a cloth with an inadequate repulsion.
A fiber with an excessively oriented surface has a drawback of a deteriorated dyeability because the highly oriented surface inhibits diffusion of a dye during a dyeing process.
JP-A 61-199707 has described a spinning process using a coagulation bath with a sufficiently higher concentration within a concentration range that a skin layer does not form. However, when using an aqueous solution of an organic solvent as a coagulation bath, a concentration range of the organic solvent that a skin layer does not form is quite higher, so that a coagulation rate becomes too late to increase a drawing rate of the coagulated filament, leading not only to an extremely lower yield but also to problems such as irregularities and fusion between fibers.
In home furnishing applications, particularly for a high-pile or boa, a cross section of a fiber is changed for providing hand feeling closer to animal hair. In these applications, good brushing effect, higher flexibility, softness, etc. are required. Brushing effect is more improved as a friction on a fiber surface is lower. It is thus believed that a dull material in which an additive such as titanium dioxide is used for emphasizing brightness generally exhibits an improved brushing effect. In the technique, color-developing properties of an acrylic fiber are, however, hampered by the additive.
JP-A 11-21769 has disclosed a technique that apparent luster and fiber color-developing are chosen as appropriate and an organopolysiloxane is bound to give slimy and smooth touch like an animal hair to the fiber surface. In the technique, while slimy and smooth touch is emphasized, the fiber may have poor softness and color-developing properties. It is necessary for an acrylic fiber with reduced luster, good color-developing properties and good brushing effect that its surface is not smoothed but a contact area between fibers is reduced when it is processed to be a pile or boa cloth, by deliberately corrugating the fiber surface. For hand feeling, a fiber well-balanced in its strength and elongation is required. In the light of these conditions, JP-A 64-33210 has disclosed a process for preparing a dry acrylic fiber with more natural luster by corrugating a fiber surface. In the process, a spinneret, however, has an orifice hole of special shape to corrugate the surface. Thus, the fiber surface corrugation is considerably limited.
Flexibility and softness in a boa or high pile may be achieved by combining several types of fibers with different cross sections. It is believed that typically a flat or Y-shaped cross section of an acrylic fiber is effective for achieving the above properties. In particular, an acrylic fiber with a Y-shaped cross section gives soft hand feeling because its tip is split while having good flexibility because it retains a Y-shaped cross section in its root.
In the acrylic fiber disclosed in JP-A 10-251915, a monofilament 20 has a substantially Y-shaped cross section where three radially extending rectangular arms 21 are jointed with a jointing angle of 120xc2x0 as shown in FIG. 7. In the joint of these arms 21, openings K1 or holes K2 are formed for adjusting the joint length c to be 30 to 95% of its width d. It allows the filament to be easily split along a longitudinal direction to realize soft hand feeling. In the acrylic fiber disclosed in the patent application, a filament may be split before polisher processing a boa or high pile due to the openings K1 or the holes K2 formed in the joint. Thus, it may result in, for example, generating fluffs during spinning. Furthermore, the fiber may not be easily dried due to water trapped in the openings K1 or the holes K2, leading to a longer drying step during spinning the fiber and thus to a reduced productivity.
An objective of this invention is to provide, for a garment material, an acrylic fiber which has even orientation in its surface and inside, gives a staple fiber with adequate elasticity to provide a cloth with a repulsion; and to provide the fiber which exhibits good physical properties such as a strength, an elongation and dyeability and exhibits softness by modifying its surface shape.
Another objective of this invention is to provide, for a home furnishing material, an acrylic synthetic fiber which has good color-developing properties with reduced luster and good brushing effect, and an acrylic synthetic fiber which retains the status where a plurality of flat arms radially extending from a center along a longitudinal direction are jointed together and the fiber tip can be readily split by applying a mechanical force during processing into a fluffy product.
Another objective of this invention is to provide a process for easily and satisfactorily manufacturing an acrylic fiber which has even orientation in its surface and inside and exhibits good properties such as a strength, an elongation and dyeability, by, during preparing a coagulated filament, controlling the thickness of a skin layer of the coagulated filament to provide a fiber evenly coagulated to its inside, i.e., by preventing a solvent inside the fiber from being inadequately diffused and thus preventing the solvent from being quickly diffused during washing.
The first aspect of this invention is directed to an acrylic fiber (a) consisting of an acrylonitrile polymer comprising an acrylonitrile unit in at least 80 wt % and less than 95 wt %, (b) having a monofilament dry strength of 2.5 to 4.0 cN/dtex, (c) having a monofilament dry elongation of 35 to 50%, and (d) forming a crack with a length of 20 xcexcm or more in its tension rupture lateral surface along the filament axis direction when rupturing the monofilament in a tension test.
The second aspect of this invention is directed to an acrylic fiber (a) comprising corrugations on its surface, (b) having an average tilt angle of 15 to 20xc2x0 between two adjacent corrugations in a cross section vertical to the fiber axis direction, (c) having a maximum level difference of 0.15 to 0.35 xcexcm between the bottom and the top of the corrugations, and (d) exhibiting a lusteriness of 10 to 20% in a lusteriness determination method for a 45xc2x0 mirror surface for a fiber bundle surface.
In one embodiment of the second aspect of this invention, the acrylic fiber (e) consists of an acrylonitrile polymer comprising an acrylonitrile unit in at least 80 wt % and less than 95 wt %, (f) has a monofilament dry strength of 2.0 to 4.0 cN/dtex, (g) has a monofilament dry elongation of 15 to 40%, and (h) forms a crack with a length of 20 xcexcm or more in its tension rupture lateral surface along the filament axis direction when rupturing the monofilament in a tension test.
The third aspect of this invention is directed to an acrylic fiber (a) comprising a plurality of flat arms radially extending from a center along a longitudinal direction and (b) forming a crack with a length of 200 xcexcm or more in the center of its tension rupture lateral surface along the filament axis direction when rupturing the monofilament in a tension test.
In one embodiment of the third aspect of this invention, the acrylic fiber (c) consists of an acrylonitrile polymer comprising an acrylonitrile unit in at least 80 wt % and less than 95 wt %, (d) has a monofilament dry strength of 2.0 to 4.0 cN/dtex, and (e) has a monofilament dry elongation of 15 to 40%.
This invention further provides a process for manufacturing an acrylic fiber comprising the steps of: discharging a spinning feed solution comprising an acrylonitrile polymer comprising 80 wt % or more and less than 95 wt % of acrylonitrile unit in an organic solvent, into the first coagulation bath consisting of an aqueous organic solvent solution at 30 to 50xc2x0 C. containing 20 to 70 wt % of an organic solvent which may be the same as or different from the organic solvent for the spinning feed solution, to form a coagulated filament; drawing the filament from the first coagulation bath at a rate of 0.3 to 2.0 times of the discharge linear velocity of the spinning feed solution; stretching the filament by 1.1 to 2.0 times in the second coagulation bath consisting of an aqueous organic solvent solution at 30 to 50xc2x0 C. containing 20 to 70 wt % of an organic solvent which may be the same as or different from any of the two organic solvents; and subsequently conducting wet heat stretching of the filament by three times or more.
In one embodiment of the above manufacturing process, there is provided a process where the concentration of the organic solvent in the first coagulation bath is 40 to 70 wt %; the drawing rate of a coagulated filament from the first coagulation bath is 0.3 to 0.6 times of the discharge linear velocity of the spinning feed solution; and the concentration of the organic solvent in the second coagulation bath is 40 to 70 wt %.
In another embodiment of the above manufacturing process, there is provided a process where the concentration of the organic solvent in the first coagulation bath is 20 to 60 wt %; the drawing rate of a coagulated filament from the first coagulation bath is 0.6 to 2.0 times of the discharge linear velocity of the spinning feed solution; and the concentration of the organic solvent in the second coagulation bath is 20 to 60 wt %.
It is preferable in the manufacturing processes of this invention that the organic solvents in the spinning feed solution, the first coagulation bath and the second coagulation bath are dimethylacetamide and the first and the second coagulation bathes are at the same temperature and have the same composition.